The present invention relates to a new vacuum circuit breaker, and a vacuum bulb and a vacuum bulb electrode used for the vacuum circuit breaker.
Vacuum circuit breakers each contain an electrode structure composed of a pair of a fixed electrode and a movable electrode. Each of the fixed electrode and movable electrode has four parts: an arc electrode, an arc electrode supporting member, a coil electrode connected to the arc electrode supporting member, and an electrode rod provided on an end of the coil electrode.
An arc electrode is directly exposed to arc each time it switchingly breaks a high voltage and a high current. In general, an arc electrode is required to satisfy basic characteristics such as a large breaking capacity, high withstand voltage, small contact resistance (high electric conductivity), high fusion resistance, small wastage of a contact, and small chopped current. However, it is difficult for an arc electrode to satisfy all of these characteristics, and consequently, an arc electrode is generally made from a material selected to satisfy characteristics particularly important for the application and to sacrifice other ones to some extent. A method of manufacturing an arc electrode material suitable for breaking a large current and a high voltage is disclosed in Japanese Patent Laid-open No. Sho 63-96204, wherein Cu is filtrated in a skeleton of Cr or Cr--Cu. Such a method is also disclosed in Japanese Patent Publication No. Sho 50-21670.
In the above method, to enhance the fusion resistance and reduce the chopped current, it may be considered to filtrate Cu added with a low melting point metal such as Pb, Bi, Te or Sb in a skeleton of Cr or Cr--Cu for uniformly dispersing the low melting point metal such as Pb in the skeleton; however, it is difficult to realize such a method because of a large difference in specific gravity between Cr or Cr--Cu and the low melting point metal.
Further, an arc electrode formed of a sintered body or an ingot added with a low melting point metal such as Pb, Bi, Te or Sb is poor in brazing characteristic with an electrode supporting member. As a result, when such an arc electrode is brazed with the arc electrode supporting member, the strength of a brazing interface therebetween is weaken.
An arc electrode supporting member, which is used mainly for reinforcing an arc electrode, exhibits another effect of generating a vertical magnetic field if it is formed into a shape suitable therefor. The arc electrode supporting member is made from pure Cu having a preferable conductivity.
A coil electrode is provided mainly for allowing an arc electrode to generate a vertical magnetic field and letting the arc generated from the arc electrode due to the field be diffused over the arc electrode, and also for forcibly breaking the arc. For this purpose, the coil electrode is formed into a shape suitable therefor. As disclosed in Japanese Patent Publication Hei 3-17335, the coil electrode also serves as a member for reinforcing an arc electrode and an arc electrode supporting member. The coil electrode is made from the same material as that of an arc supporting member, that is, pure Cu.
The electrode structure composed of an arc electrode, arc electrode supporting member, coil electrode and electrode rod is manufactured in accordance with steps of preparing an arc electrode and machining it; machining an arc electrode supporting member, coil electrode and electrode rod; and assembling these parts, followed by brazing.
An arc electrode is prepared by a power metallurgical process of mixing powders of Cr, Cu, W, Co, Mo, V, and/or Nb or an alloy thereof in a specific composition, compressing the mixture into a compact having a specific shape and a specific porosity, sintering the compact, and filtrating molten Cu or Cu alloy in a skeleton of the sintered body. In the above process, in the sintering step, a sinter body having the density of 100% may be produced. The sintered body thus obtained is then machined into a specific shape, to prepare an arc electrode.
Each of the arc electrode supporting member, coil electrode and electrode rod is machined from a pure Cu material into a specific shape suitable for generation of a vertical magnetic field.
The parts thus prepared are assembled, followed by brazing, to obtain an electrode structure. Here, brazing is performed by inserting a brazer having a wettability between the arc electrode, arc electrode supporting member, coil electrode and electrode rod, and heating them in a vacuum or a reducing atmosphere. Accordingly, in manufacture of the electrode structure assembled by brazing, it takes a lot of labor and time in machining each part and alignment of parts for brazing. Further, in brazing between the arc electrode containing a low melting point metal such as Pb and the arc electrode supporting member in accordance with the conventional method, there occurs a disadvantage that the wettability of brazer is deteriorated because of segmentation of Pb in the arc electrode and the presence of Pb at the interface between the arc electrode and the arc electrode supporting member. In addition, for an electrode structure having a large diameter, there may occur breakage and/or slip-off of an electrode material due to defective brazing. Therefore, the electrode structure manufacture in accordance with the conventional method is poor in uniformity of electrode characteristic, reliability, and safety.
Recently, along with the advanced development of a material, an attempt has been made to switchingly break a large current and a high voltage by suitably setting a design specification of vacuum circuit. For example, a breaking performance is improved by increasing an input speed. The increased input speed, however, increases a contact force between arc electrodes and also gives a impact stress on the entire electrode upon opening/closing the electrode structure. This causes deformation of the electrode material with time. In general, an arc electrode is made from a high strength material being good in breaking characteristic and fusion resistance; however, each of an arc electrode supporting member, coil electrode and electrode rod is made from pure Cu which is very small in proof stress. Further, since the arc electrode supporting member is provided with grooves in the direction of cross-section for generating a vertical magnetic field, and therefore, it cannot withstand an impact stress and is deformed with time. The deformation of the electrode material causes an inconvenience in opening/closing of the electrode structure, fusion, breakage and/or slip-off of an arc electrode, and a trouble of emergent opening/closing of the electrode structure.